Marine paleoseismology in the Western Gulf of Corinth (Greece) for the last 500 years

Related to the Gulf of Corinth rifting, five earthquakes of magnitude greater than 5.8 occurred in the last 35 years. Consequently, the question of earthquake (EQ) hazard is particularly relevant. Onland, paleoseismological data are scarce and offshore data were absent before the present study. We investigated recent sediments bounding three well-defined major seismogenic faults. We retrieved 12 gravity cores from 50 to 85 cm long in three distinct sites: the southern shelf (40 to 50 m deep), a 180 m deep sub-basin, and a transect from the southern coast to the center of the gulf. We performed grain size analysis, magnetic susceptibility, loss on ignition and geochemical (X-Ray Fluorescence) measurements on cores from each site. We sought to identify layers potentially attributed to EQ-related processes like liquefaction and tsunamis for the sites on the shelves or mass transport and turbidity currents for the basins. Chronology is based on 137Cs (Atmospheric Nuclear Experiments) and 210Pb decay. Considering sedimentation rates estimates in these areas, the longer cores record about 500 years of sedimentary archives. On the southern shelf, 3 coarser layers have been identified at identical depth in 3 cores. 210Pb decay show erosion just under the first event that we attributed to the 1995 tsunami (backwash flow deposit). In the 180m deep sub-basin, among 3 clear grain-size peaks, two have been attributed to the 1817 Aegion EQ and the 1660 Galaxidi EQ. In last site, 10 “events” (grain-size and Zr/Rb peaks) have been identified in the deepest part of the transect 4 on the shelf. Their analysis is in progress, as well as paleomagnetic measurements.